If you search this forum, you will find all the information.
It is has been long understood that what the charges the carriers add bears no relationship to what they are charged - it is simply what they can get away with. Evidence shows that they can get away with a lot!
The pax will, ultimately, look at the bottom line of cost and decide if that is a price worth paying. They know that £/€1 fare will land up being anything from £/€ 25 to 50 and so on.
Thus far, the rules imposed by law have not forced them to spell out the exact make up of these charges. Even if they did - it would not make much mind. The bottom line price is all that is relevant although do not take my view one that this does not matter! I think it reprehensible that sellers are allowed to do this and have pointed out before the way that the AirMiles company do the same.